Today, most heavy duty trucks and many other vehicles are powered by a diesel engine. The volatility of diesel fuel prices compared to the relative stability of contract natural gas prices, provides both budgetary confidence and reduction of diesel fuel costs when used as a secondary fuel introduced into a diesel engine.
There is an advantage of utilizing a gaseous secondary fuel (liquefied or compressed and stored in the vehicle) to offset the usage of diesel fuel, as many such gases have a lower cost per unit of energy than diesel fuel. Examples of such gaseous fuels are liquid propane gas, liquid natural gas, compressed natural gas and compressed hydrogen gas.
There have been many attempts to supplement a secondary gaseous fuel for diesel fuel in the applications mentioned above. For example, liquid propane gas has been used as an alternative fuel in spark ignited engines using kits that provide total substitution of gaseous propane for gasoline for many years being very successful. However, when introduction is made of a gaseous fuel into a diesel engine whereby the gaseous propane is introduced to a single point injector or multiple injection points into the engine intake manifold or intake air plenum of the diesel engine. The theory is that the increase added fuel (secondary fuel) will increase the engine speed/power beyond what the engine controller senses is required or requested and thus the stock engine controller will automatically reduce the volume of the primary diesel fuel. The stock engine controller acts, in this case, as a governor reducing the amount of primary diesel fuel provided to the diesel injectors of the diesel engine, thus managing power output of the engine. In theory, the reduction in diesel fuel injection produces a net cost saving. However, these types of fumigation or multi-port systems no matter the level of sophistication cannot control the volume of secondary fuel being ingested by each cylinder of a multi-cylinder engine. These type fumigation and multi-port fumigation system can control a basic volume ratio of secondary fuel to a primary, but cannot control the actual volume of secondary fuel actually entering a specific cylinder of a multi-cylinder diesel engine.
Another method of reducing diesel (primary fuel) injected into the engine cylinder is done by remapping the primary diesel fuel delivery map parameters of the stock engine controller. This is not desirable for several reasons including cost and variances in OEM fuel maps that regulate speed and power output of various engines in an OEM engine manufacturer's engine family, but most important the OEM fuel map is extremely difficult to duplicate exactly, thus use of primary fuel remapping causes an engine to be under fueled or over fueled. Both fueling conditions are undesirable and can harm the diesel engine.
What is required by the heavy duty diesel users is a blended fuel system that will add a secondary fuel precisely to each cylinder seamlessly utilizing the stock engine controller and a secondary controller/processor which measures to within one millionth of a second the OEM fuel mapping (primary diesel fuel injection signal pulse) for each cylinder diesel injection event of a multi-cylinder engine to compute the BTU energy level of the diesel primary fuel being injected, which processes that primary diesel fuel signal to construct an injection ratio (e.g. a replacement ratio) of a secondary gaseous fuel based solely on the BTU energy level of the last injection event of the primary diesel fuel and the time available to inject the secondary gaseous fuel during a specific cylinder's next intake cycle and modifies (shortens) the pulse width of the next primary diesel fuel injection so that the exact BTU energy level designated by the original engine fuel map for a specific cylinder is met using a combination of secondary gaseous BTU energy content plus the BTU energy content of the next primary diesel fuel injection.